Alternative Names

Culture - blood

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

The sample is sent to a laboratory, where it is placed in a special dish and watched to see if germs grow. This is called a culture. Most cultures check for bacteria. If bacteria does grow, further tests will be done to identify the specific type.

A gram stain may also be done. A gram stain is a method of identifying microorganisms (bacteria) using a special series of stains (colors). For example, see skin lesion gram stain.

Why the test is performed

Your doctor may order this test if you have symptoms of a serious blood infection. Symptoms include high fever, chills, rapid breathing and heart rate, confusion, and very low blood pressure. See also: bacteremia or septicemia

The blood culture will help identify the type of bacteria causing the infection. This helps the doctor determine your best course of treatment.

Normal Values

A normal value means that no bacteria or other germs were seen in your blood sample.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

An abnormal (positive) result usually means that you have an infection called sepsis. Sepsis is a severe illness in which your blood is overwhelmed by bacteria. If you have sepsis, you will be admitted to a hospital.

Other types of germs, such as a fungus or a virus, may also be found in a blood culture.

Sometimes, an abnormal result can be due to contamination. This means bacteria may be found, but it came from your skin or from the lab equipment, instead of your blood. This is called a false-positive result. It means you do not have a true infection.

What the risks are

The blood culture is done in a lab. There are no risks to the patient. For information on risks related to giving a blood sample, see venipuncture.

Special considerations

A bacterial blood infection sometimes comes and goes, so a series of three blood cultures may be done to confirm results.